The invention relates to method and apparatus for testing the abradability of materials.
For some products, the abradability of the materials used to make them is an important measure of their durability and wear characteristics. For example, the abradability of the rubber used to make tire tread gives an indication of the life of the tire in terms of mileage, and may be an indication of the tire""s resistance to irregular wear. In U.S. Pat. No. 5,113,688, issued May 19, 1992, a laboratory traction test is described wherein abradability, although of not primary importance, is recognized as one of the components in the traction properties of the rubber. Some of the art cited as references in that patent, namely U.S. Pat. Nos. 1,327,838; 1,490,603; 2,058,805; 3,638,230; 3,982,427; and 4,275,600; relate to the abradability of rubber compositions.
Burr et al., in U.S. Pat. No. 4,404,840 teach a device for evaluating the abrasive wear of elastomeric o-ring materials. In the device, a segment of a small diameter o-ring is held in contact with a rotating cylindrical disk. The disk is mounted to rotate on its longitudinal axis, and the o-ring segment and the cylinder are immersed in an abrasive fluid. Abrasive particles in the fluid are pulled between the wear surfaces, causing removal of surface materials, especially that of the o-ring. The oring segment is weighed before and after testing, and the amount of wear is calculated. Service loads or pressure are simulated by means of a cable and weight system urging the o-ring against the wear disk surface by means of a lever arm pulley arrangement.
Yuan, in U.S. Pat. No. 5,689,058 teaches a friction-material evaluation apparatus, especially adapted for testing brake friction material. The apparatus has a movable table which carries both a variable-speed electric motor that drives a brake rotor, and a reversible electric motor that may be actuated to advance the brake rotor into friction contact with the test material with a normal force that correlates to the output torque of the reversible electric motor. A heater 60 is positioned in surrounding relation to the hub of rotor subassembly 52, and preferably includes a heat sensor which detects the rotor surface temperature.
In the prior art, abradability was measured by dragging or pushing a rubber sample over a rough surface such as sandpaper, under a certain load for a specific distance. The abradability of the rubber sample was measured by weighing the sample before dragging it over the rough surface, and weighing the sample after dragging it over the rough surface, and the abradability of the compound was indicated by the volume loss per unit energy input. Such tests were ordinaily carried out at room temperature, and temperature factors relating to abradability were not usually considered.
It is the object of the present invention to provide an apparatus whereby abradability of a compound can be measured under different loads, under different temperatures, and under different atmospheric conditions. Also, the abrasion surface may be varied using the apparatus of the invention so that a profile of a particular compound can be obtained relating to its abradability over a broad range of surfaces.
Other objects of the invention will be apparent from the following description and claims.
An apparatus for abrasion testing comprises a rotatable drum having abrasive means on its surface, a variable speed motor associated with the drum for varying the speed of the drum, a sample holder in close proximity to the drum for contacting a sample with the drum, and a force transducer associated with the sample holder for measuring the energy expended when a sample is in contact with the drum. The apparatus may further comprise an environmental chamber encompassing the drum and the sample for testing at different temperatures and different atmospheres.
In the illustrated embodiment, the apparatus further comprises rotating means for rotating a sample relative to the drum, and translating means for moving the sample axially with respect to the drum. Accordingly, at least three axes of motion of the sample relative to the drum are possible using the apparatus. All axes of motion can be used simultaneously, or testing can be carried out on one axis of motion, as desired.
A personal computer can be used for controlling the rate of rotation of the drum, the speed of translation of the sample, and the speed of rotation of the sample. The personal computer can also be used to control the temperature and/or atmosphere in the environmental chamber.
The abrasive means of the drum may comprise an abrasive pattern etched, carved, stamped or molded onto the surface of the drum, and in one embodiment comprises a 10 to 300 mesh abrasive paper attached to said drum.
Load means may be provided for varying the load on said sample from 1 N to 25 N.
The temperature control means may control the temperature surrounding the drum and the sample from xe2x88x92100 C.xc2x0 to 200 C.xc2x0.
Also, the atmosphere control means may provide an atmosphere surrounding the drum and sample comprising substantial amounts of a gas selected from the group comprising ozone, air, and water vapor.
The variable speed motor drives the rotation of the drum at from 2 to 100 revolutions per minute (rpm).
The force transducer is a multiaxial force transducer capable of measuring energy expended between the drum and the sample in multiple directions. In the illustrated embodiment, the multiaxial force transducer is capable of measuring energy expended in the direction of rotation of the drum and in a direction perpendicular to the rotation of the drum.
In the illustrated embodiment, the sample rotating means is a cable wrapped around a spindle carrying the sample, and the rotating means has associated therewith a variable speed control for varying the speed of rotation of the sample.
Also provided is a method for measuring the abrasive properties of a material comprising the steps of (a) providing an apparatus having a rotatable drum having abrasive means on its surface, a variable speed motor associated with the drum for varying the speed of the drum, a sample holder in close proximity to the drum for contacting a sample with the drum, and a force transducer associated with the sample holder for measuring the energy expended when a sample is in contact with the drum, (b) weighing a sample to determine its initial weight, (c) bringing a sample into contact with the drum at a specified load and a specified speed, (d) measuring the energy expended between the sample and the drum, (e) removing the sample from the test apparatus after a specified period of time and weighing the sample, and (e comparing the weight of the sample after testing with the initial weight of the sample.
In the method the sample may be rotated while the sample is in contact with a rotating drum.
The method may further comprise the steps of (a) providing the apparatus with an environmental chamber capable of controlling temperature and or atmosphere encompassing the drum and the sample, (b) repeating steps a-f above under different environmental conditions, and (c) comparing results achieved under different conditions for the same sample and for comparison samples.
The method further comprises the steps of comparing data with respect to weight loss and energy expended to estimate wear and traction properties of a sample.